By default a standalone ESXi host will keep 1 hours worth of performance data. vCenter Server will allow you to capture performance data long term, but if you have just the standalone ESXi host you can extend the capture of performance data to 36 hours with just a simple configuration change. This change will require SSH or console access and is not supported.

1) Open the file /etc/vmware/hostd/config.xml. Change the portion in bold from false to true. Note that you can also change the collection interval for realtime stats from 20 seconds to another value. One other important thing to note is that this data is stored in /var/lib/vmware/hostd/stats which is on the RAM drive that ESXi creates when it boots. If you restart the host, your "past day" data will be lost. This file is backed up to state.tgz (local.tgz for ESXi Embedded) so the change will survive a reboot.

2) Once the above change is made, you can either restart the host or run the console command services.sh restart. When you reconnect with the VI client, you'll notice the PastDay option when viewing performance data. It will take several minutes before any data is collected for the past day view. When you select past day, you will only be able to view the full 36 hours as the From and To options will be greyed out.

After you have made the change the configuration of the file /var/lib/vmware/hostd/stats/hostAgentStats.xml will be changed to include the interval_id of 0001 which defines past day collection settings. The new file hostAgentsStats-300.stats will also be created to store this data.